However, any benefit from the oils is lost after more than one hour’s exposure, which, in fact, may be even harmful to cardiovascular health.

A study of 100 healthy spa centre workers in Taipei, Taiwan, found that their blood pressure and heart rate fell when they sat in a room infused with essential oil vapours from an ultrasonic ioniser for between 15 and 60 minutes.

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Each of the participants visited the study centre three times over three weeks to sit in a small room that had been pumped with 100 per cent bergamot oil.

But over one hour’s exposure to the oils and the level of volatile organic compounds (VOC) from them was associated with an increased blood pressure and heart rate, leading the study’s researchers to say that “prolonged exposure for longer than one hour to essential oils may be harmful to cardiovascular health in young, healthy subjects”.

Dr Kai-Jen Chuang from Taipei Medical University in Taiwan, who led the study, said: “Our results suggest that exposure to essential oil for one hour would be effective in reducing heart rate and blood pressure.

“However, the most interesting finding of our study is that exposure to essential oil for over an hour was associated with elevated blood pressure and heart rate.”

Dr Chuang said aromatherapy had been associated with some healing properties for centuries and that even being in contact with essential oil vapours from fragrant candles had also been found to reduce test-taking anxiety among nursing school students in the USA.

The research is published in the November 29 edition of the European Journal of Cardiovascular Preventative Cardiology.

About Jayne Howarth

Jayne Howarth is a freelance journalist with over 20 years' experience in the industry. She worked for 15 years at The Birmingham Post and has also written for a wide variety of websites focusing on health.